Chemical Signaling, Neural Signaling, and Homeostasis Review

Flashcards covering chemical signaling mechanisms, the action potential in neurons, and homeostatic regulation of glucose, temperature, and osmoregulation.

Ligands

Chemical signals that bind to specific receptors to trigger a response in the target cell.

Quorum sensing

A process in bacteria based on intercellular communication where a behavior is triggered once the population density rises above a certain threshold.

Auto-inducer

A signaling molecule secreted by $Vibrio\,fischeri$ that diffuses between cells and binds to a receptor to induce the transcription of bioluminescence genes.

Luciferase

An enzyme produced by $Vibrio\,fischeri$ that catalyzes an oxidation reaction to release energy as greenish-blue light.

Hormones

Signaling chemicals produced by specialized glands and transported by the bloodstream to parts of the body to affect target cells with specific receptors.

Neurotransmitters

Chemicals such as acetylcholine and dopamine that transmit signals across the synaptic gap between neurons.

Cytokines

Small proteins secreted by a wide range of cells that bind to membrane receptors to trigger cascades of reactions and changes in gene expression.

Sarcoplasmic reticulum

A specialized form of endoplasmic reticulum in muscle fibers used to store high concentrations of calcium ions.

Intracellular receptors

Receptors located within the cytoplasm or nucleus that bind to non-polar signals, like steroid hormones, which can pass through the plasma membrane.

Transmembrane receptors

Receptors embedded in the plasma membrane that bind to ligands that cannot pass through the phospholipid bilayer.

G-protein coupled receptors (GPCRs)

A group of transmembrane receptors that convey signals using a G-protein composed of alpha, beta, and gamma subunits.

Adenyl cyclase

An enzyme activated by a G-protein that converts ATP in the cytoplasm into cyclic $AMP$, a secondary messenger.

Kinase

An enzyme that adds a phosphate group from an ATP to a specific molecule in a process called phosphorylation.

Tyrosine kinase

Enzymes on the tails of insulin receptors that phosphorylate each other when insulin binds, triggering the insertion of glucose transporters.

Positive feedback

A regulation pathway where the end product serves to amplify the starting point, moving the system further away from its original state.

Negative feedback

A regulation mechanism where an increase in the end product inhibits the start of the pathway to restore the original level.

Resting potential

The membrane potential maintained at $-70\,mV$ inside a neuron due to the action of the sodium-potassium pump and ion leakage.

Sodium-potassium pump

An active transport protein that pumps $3\,Na^+$ ions out and $2\,K^+$ ions into a neuron for every ATP molecule used.

Threshold potential

The critical membrane potential level of $-50\,mV$ that must be reached to trigger an all-or-nothing action potential.

Depolarization

The phase of an action potential where voltage-gated sodium channels open and $Na^+$ ions flood into the axon, reaching about $+30\,mV$.

Repolarization

The phase where sodium channels close and voltage-gated potassium channels open, allowing $K^+$ to flood out and restore a negative membrane potential.

Refractory period

The period after repolarization where the sodium-potassium pump resets the resting potential, ensuring unidirectional movement of the impulse.

Myelin sheath

An insulating coat around axons formed by Schwann cells that enables saltatory conduction by allowing impulses to jump between nodes of Ranvier.

Acetylcholinesterase

An enzyme in the synaptic gap that rapidly breaks down acetylcholine into choline and acetate to prevent continuous stimulation.

Neonicotinoid pesticides

Synthetic compounds that block synaptic transmission in insects by irreversibly binding to acetylcholine receptors.

GABA

An inhibitory neurotransmitter that binds to receptors to open chloride channels, causing hyperpolarization of the postsynaptic neuron.

Homeostasis

The regulation of the internal environment, keeping variables like body temperature and blood glucose within narrow, optimal limits.

Alpha cells

Cells in the islets of Langerhans in the pancreas that secrete glucagon when blood glucose concentrations are low.

Beta cells

Cells in the islets of Langerhans in the pancreas that secrete insulin when blood glucose concentrations are high.

Type 2 diabetes

A condition characterized by an inability of target cells to respond to insulin due to a deficiency in insulin receptors or glucose transporters.

Thyroxine

A hormone secreted by the thyroid gland that increases the metabolic rate of cells to generate heat.

Uncoupled respiration

A process in brown adipose tissue where the energy released by the oxidation of fat is transferred to heat instead of ATP production.

Ultrafiltration

The process in the Bowman's capsule where high blood pressure forces water and small solutes through a basement membrane and podocytes.

Selective reabsorption

The recovery of useful substances like glucose and amino acids from the filtrate back into the blood in the proximal convoluted tubule.

Antidiuretic hormone (ADH)

A hormone from the pituitary gland that increases water reabsorption by increasing the number of aquaporins in the collecting duct walls.

Podocytes

Cells in the Bowman's capsule with branching outgrowths that wrap around capillaries and act as a filter during ultrafiltration.